Automatic transmissions, particularly those for motor vehicles, comprise according to the prior art planetary gear sets that are shifted by means of friction and/or shift elements, such as clutches and brakes, and usually are connected to a start-up element that is subject to a slip effect and optionally provided with a direct-drive clutch, such as a hydrodynamic torque converter or fluid coupling.
Automatic transmissions of this kind have been described extensively in the prior art and are subject to continuous development and improvement. Correspondingly, these transmissions are intended to provide an adequate number of forward gears and at least one reverse gear, as well as step changes that are very well suited for motor vehicles with a high overall gear ratio and favorable step changes. Furthermore, they are to allow for a high start-up ratio in the forward direction, and contain a direct gear. Moreover, automatic transmissions should not require any great structural complexity and a large number of shift elements, wherein, for a sequential gear-shift, only one given shift element is to be activated and one shift element deactivated, respectively.
An automatic transmission of this kind is known, for example, from DE 199 12 480 B4 filed by the applicant. It comprises three single carrier planetary gear sets as well as three brakes and two clutches for shifting six forward gears and one reverse gear, one input shaft and one output shaft, wherein the carrier of the first planetary gear set is continuously connected to the ring gear of the second planetary gear set and the carrier of the second planetary gear set to the ring gear of the third planetary gear set, and the input shaft is directly connected to the sun gear of the second planetary gear set.
Further, the known transmission provides that the input shaft can be connected to the sun gear of the first planetary gear set by means of the first clutch and to the carrier of the first planetary gear set by means of the second clutch, wherein the sun gear of the first planetary gear set can be connected to the housing of the transmission by means of the first brake and the carrier of the first planetary gear set can be connected to the housing of the transmission by means of the second brake, and wherein the sun gear of the third planetary gear set can be connected to the housing of the transmission by means of the third brake. The output shaft of the transmission is continuously connected to the carrier of the third planetary gear set and to the ring gear of the first planetary gear set.